The present invention relates to a power transmission for automotive vehicles, and more particularly to a power transfer device for four-wheel drive in combination with a power transmission transversely assembled to a cylinder block of an internal combustion engine.
A conventional power transfer device for four-wheel drive as described above has been proposed as is illustrated in FIG. 3 of the accompanying drawings. The power transfer device is adapted to a conventional power transmission for front-wheel drive, wherein an intermediate differential gear unit 1 is substituted for an original differential gear unit for front-wheel drive to split the driving power from the transmission into two delivery paths respectively for front-wheel drive and rear-wheel drive and wherein a trasnfer casing 3 is secured at its one side seating face to a transmission casing 2 to contain a differential gear unit 4 for front-wheel drive and an output gearing including gears 5, 6 and 7 for rear-wheel drive. In such an arrangement, the differential gear unit 4 is spaced in a distance L from the intermediate differential gear unit 1. For this reason, vibration system of front-wheel axles 8 and 9 connected to the differential gear unit 4 becomes greatly different from that of front wheel axles connected to the original differential gear unit. This means that is is required to change component parts of the front suspension system for the vehicle. Furthermore, the differential gear unit 4 is supported at its one end by a tapered roller bearing 12 carried on the transfer casing 3, while the gear 5 is supported also at its one end by a tapered roller bearing 10 carried on the transfer casing 3 and connected to the other end of unit 4 by means of a tapered roller bearing 11. In such a mounting construction, the support of gear 5 is insufficient in strength, and durability of the intermediate roller bearing 11 will lower due to the load acting thereto in operation. Additionally, undesired vibration noises will occur due to such unstable support of the intermediate roller bearing 11. When the differential gear unit 4 is connected to the gear 5 to lock the intermediate differential gear unit 1, there will occur defacement of the intermediate roller bearing 11 due to an excessive load acting thereto.